Field of the Invention
The present invention relates to a vehicle, such as a utility vehicle, equipped with an electric transaxle integrated with an axle and an electric motor for driving the axle. Also, the present invention relates to a transmission assembly adapted to be driven by an engine and provided with an electric motor for assisting the engine. Especially, the transmission assembly includes a continuously variable belt transmission (CVT).
Background Art
As disclosed by U.S. Pat. No. 7,926,387 B, a conventional utility vehicle is equipped with a rear transaxle under a load carrying bed. The rear transaxle includes a housing incorporating a gear train and a differential. An engine and a hydrostatic stepless transmission (HST) are directly mounted on the housing. The rear transaxle supports rear wheel axles. A front transaxle supporting front wheel axles is separated from the rear transaxle and is disposed at a front portion of the vehicle forward of the load carrying bed. A housing of the front transaxle incorporates a differential, and a PTO shaft projects from the housing of the rear transaxle so as to be drivingly connected to the differential of the front transaxle via a propeller shaft. Power of the engine is transmitted to the rear wheel axles and the front wheel axles via the HST and the gear train.
As disclosed by U.S. Pat. No. 7,946,953 B and US 2010/0263958 A, another conventional engine utility vehicle is equipped with a mid-shipped engine, a rear transaxle casing supporting right and left rear wheels, a front transaxle casing supporting right and left front wheels, and a transmission for distributing power of the engine between the front and rear transaxle casings. Each of the front and rear transaxle casings incorporates a differential unit differentially connecting the right and left front or rear wheels to each other. The transmission is a combination of a hydrostatic stepless transmission (HST) and a gear transmission, or a combination of a belt transmission serving as a continuously variable transmission (CVT) and a gear transmission, for example.
Some types of sports utility vehicle are mainly used for hunting purposes. Silence is a matter of great importance for hunting vehicles. Therefore, many utility vehicles used for hunting are electric vehicles equipped with electric motors. However, hunting vehicles are sometimes desired to have great power, such as engine power, for high-speed traveling on roads, for high-torque traveling on rough fields, or for other purposes. Further, recently, people dwelling in residential districts have greatly demanded utility vehicles because the utility vehicles are convenient for various daily living tasks, e.g., for taking children to and from school or kindergarten bus stops. The residents desire silence, compactness and economy of the utility vehicles. An electric motor is an effective means for achieving the silence. However, the residents also sometimes desire the utility vehicles to have great power, such as engine power, for high-speed traveling on roads or other purposes.
To satisfy the above-mentioned desires, a utility vehicle is expected to have an engine and an electric motor and to be configured so that either/both electric power or/and engine power can be optionally selected as power for driving the utility vehicle, while ensuring compactness in structure and economy in structure and in power consumption.
Further, as disclosed by US 2010/0120565 A, there is a well-known conventional vehicle equipped with a transmission assembly that includes a belt transmission driven by an engine, and a gear transmission driven by the belt transmission. This belt transmission is a continuously variable transmission (CVT) that automatically changes its speed ratio in correspondence to an output speed of the engine and an actual traveling speed of the vehicle. The defect of the CVT is a delay of reduction of output speed. In other words, a vehicle equipped with a multi-speed gear transmission can greatly reduce the traveling speed by a speed-down shift operation of the gear transmission. Such an efficient reduction of traveling speed is called “engine brake”, however, the CVT cannot serve as the engine brake in at least a part of its overall speed shift range. As a result, the CVT needs to apply a mechanical brake to efficiently reduce a traveling speed of a vehicle in such a case where the vehicle descends a slope.